You might want to take a good look at the API.
http://java.sun.com/j2se/1.5.0/docs/api/javax/swing/JApplet.html
I think of JApplet as similar to a JFrame more than a JPanel. Both implement the RootPaneContainer interface (along with JDialog) and are top-most containers of an app. So just like a JFrame, you can add panels to the JApplet's contentPane through getContentPane.add().